Radio News March 2018

WHEAT:NEWS RADIO March 2018 Vol 9, No 3

Stereo Miking Technique You Should Know

Playing the middle against the sides

By Scott Johnson

Every engineer finds himself in this situation from time to time. You’ve got a small local acoustic band visiting your morning drive talk show, and during the interview they want to perform one of their songs live on the air. You don’t have the time or gear to mic up every voice and instrument separately, so ideally what you want is a nice, live-sounding stereo pickup of the group as a whole. But you also want to make sure it’s mono-compatible; even in the 21st century, there are still radios out there with one speaker, and a hollow-sounding mono signal just won’t do.

There is a very wide array of techniques for miking a sound source in stereo. But only one is truly suitable for our needs, for an equally wide array of reasons.

One common technique is the spaced pair, where you place two microphones far apart, just as the early experimenters with stereo sound did. This results in an unnaturally wide stereo listening experience, which we might like. But when it’s collapsed to mono it’s a mess because of phase cancellation. So that one’s out.

Another method is the near-coincident pair, or ORTF method. (The letters stand for the Office de Radiodiffusion Télévision Française, where the method was invented.) This technique uses two cardioid microphones with their capsules about as far apart as human ears are, and angled at 110 degrees. It produces a very natural sound and is fairly compatible with mono, but the distance between the microphones can cause cancellation at some frequencies.

Then there’s the coincident pair. Angling two cardioid mics at 90 degrees with their capsules right on top of each other gives us an expansive pickup pattern, and also prevents virtually all phase cancellation issues since all sounds arrive at both microphones at exactly the same time. The disadvantage here is that the stereo image doesn’t sound as wide or natural. The mic patterns overlap quite a bit, and our ears aren’t perfectly coincident.

So how do we get the wonderful width and sense of depth of an ORTF pair or even the exaggerated image of a spaced pair, but achieve the same perfect mono coherence as the coincident pair? The best way is with a technique called mid-side (variously abbreviated as M-S, M/S, or just MS) miking. The technique was developed by EMI recording engineer Alan Blumlein, circa 1933, and it’s ideal for broadcast use because while it produces a great stereo image, it’s also totally mono-compatible.

Learn the technique and why it works...

To do this, we’re going to need two microphones. One of them should be a bidirectional microphone. A dual-diaphragm condenser like the AKG C414 is ideal, but any bidirectional microphone will suffice if it’s of reasonable quality.

The other microphone is usually a cardioid. It should be of comparable quality to the bidirectional microphone and is also usually a condenser. A Neumann KM184 is a great choice, but again, microphone selection is not critical to the technique’s success. Only the patterns matter.

The bidirectional mic is placed on a stand with its capsule facing left and right. Generally, the “front” or “positive” side of the mic faces left and we will assume that here.

The second mic is placed facing the source. For reasons of phase coherence, it should be as coincident with the other mic as possible; ideally, its capsule should rest right above the bidirectional’s capsule.

So now we have cables from two microphones headed back to the console, and that’s where we do the interesting part: matrixing these middle and sides signals to a left/right pair. We’ll need three faders to do this.

On fader 1, we’ll assign the middle (cardioid) microphone. We’ll set it to a nominal level and pan it center on our stereo bus.

On fader 2, we’ll assign the bidirectional (sides) microphone. We’ll pan it to the left on our stereo bus.

On fader 3, we’ll assign the sides microphone again. (On an analog console, we can do this with a Y cable, or by way of the patch bay.) On this fader, we REVERSE the phase (polarity) of the incoming signal and pan it to the right.

Now all we have to do is set the trims on faders 2 and 3 to a nominal level, ensure they’re both set to exactly the same level, and bring up all three faders. You’ll be capturing a very wide, rich stereo field thanks to the combined patterns of the three microphones.

Here’s the best part. Try moving the level of the middle mic. As you pull it down, you’ll sense that the stereo image widens. If you push it up higher, the stereo image will narrow.

How does it work? For purposes of discussion, let’s call the middle mic M and the sides mike S.

The left channel of the stereo bus is receiving M + S, meaning that the sounds arriving at the left side of the sides microphone are being added to the middle mic signal.

The right channel is seeing M – S, meaning that sounds arriving at the right (back) side of the sides mic are being added to the middle mic signal. We flipped the polarity on this fader so that the sounds arriving at the back (right side) of the bidirectional mic, which are naturally of opposite polarity from the front, will again have the same polarity as the middle mic and add properly.

Signals arriving from dead center will enter both the front and back sides of the bidirectional mic at the same time, producing opposite signals that cancel, so those sounds are picked up only by the middle mic and are fed to both sides of the stereo bus.

But more importantly, because the two side mic faders are precisely level-matched and opposite in polarity, their contributions to the mix are exact opposites, and if the stereo bus is summed to mono, the sides signals will cancel out, leaving a perfectly clean mono signal from the middle mic. No mono compatibility problems can arise.

There are a couple of variations on the technique. You can try using an omnidirectional microphone for the middle channel, which makes the entire array essentially a stereo omni microphone. This can accentuate the pickup of room tone and reverberation if your room has good acoustics. You can also use a second bidirectional microphone for the middle channel with similar results, extending the pickup pattern.

The technique isn’t just for music, either. M-S miking a live shot, for example, or a speech before a live audience, has a tendency to put the viewer right in the middle of the crowd, improving overall fidelity of the experience. It’s even a good way of capturing crowd or environmental sounds that will later be mixed with a voice-over, dialogue, or an interview as stereo nat sound.

Mid-Side miking can save the engineer a great deal of time and aggravation, capturing a clean, clear, dimensional stereo image that’s ideal for television broadcast. It’s a technique every audio engineer should have tucked away in his bag of tricks.

Scott Johnson is a systems engineer and webmaster for Wheatstone. He has plenty of mic techniques up his sleeve as a lifelong audio engineer. When he’s not experimenting with Wheatstone mixers and mic processors, he can be found at the local community theater mixing sound for the latest production.

3 Killer Bass Tips

While cranking up the bass can give a station incredible punch and a unique on-the-dial identity, it's also one of the easiest things to overdo. It's amazing how a couple of innocent looking GUI knobs can cause so much trouble for a listener's radio. Here are three important things to keep in mind before you touch that processor panel:

1. Boosting subsonic bass might make the PD's car subwoofer kick but it’ll cost you loudness on radios that lack the ability to reproduce that bass. Why? Our ears are much less sensitive to low bass than they are to mid frequencies, so that deep bass you're tempted to crank in is going to eat up LOTS of modulation to make it really kick on most radios.

2. If you have analog gear in the air chain that’s a more than a few years old, consider replacing electrolytic capacitors. This will bring back bass you’d forgotten was even possible. As electrolytic capacitors age, their value typically decreases, and they slowly, slowly, slowly destroy bass. It happens so slowly, you'll never notice it day-to-day.

3. Resist the temptation to copy a competitor's bad habits and that most especially applies to bass settings. Listen to competing stations, and keep a log of what you like and don’t like if you want, but follow your own beat. What’s really important is what your station sounds like on radios that your listeners will be using in order to listen to your audio content.

Download Our Free E-Book: Advancing AoIP for Broadcast

Putting together a new studio? Updating an existing studio?

We've put together this e-book with fresh info and some of the articles that we've authored for our website, white papers, and news that dives into some of the cool stuff you can do with a modern AoIP network like Wheatstone's WheatNet-IP.

Interesting Links

Panthers in the Factory

Our cameras followed along as new studio gear for the Carolina Panthers wound its way through our factory. Collegiate sports broadcaster IMG ordered two customized LXE consoles, some TS-4 talent stations and a few M4IP-USB mic BLADEs for a new Panthers studio that will be integrated into its large WheatNet-IP networked studio complex in Winston-Salem.

We started in the metal shop, where we found Rodney running the CNC punch press to turn out the module faceplates for the LXE. Check out the precision of this machine!

Next up, cutting and labeling custom panels that'll be used in the new Panthers studio. Here, Wheatstone's Computer Numerically Controlled laser cuts out the necessary pieces of acrylic, making openings and windows as necessary. From here the panels will go to screen printing.

As the system for the Carolina Panthers continues to make its way through our factory, piece by piece, Sylvia Artis, our test department boss, performs quality control inspection on each of the modules destined for the Panthers' LXE consoles. This thorough visual and mechanical quality control inspection ensures that every part is perfect prior to assembly.

In the metal shop, our computer-controlled laser cutter is swiftly slicing out metal plates for the Carolina Panthers’ special, custom-designed panels. The laser boasts 1,000 watts of power, and is gas-assisted. It's quite fun to watch it in action!

More Panthers...

Here’s a look at the creation of the acrylic overlays for the custom TS-4 talent stations we're building along with the LXE for the Carolina Panthers. The clear acrylic is laser-cut and screen printed on its back side, so the graphics don't wear off. There's a lot of very delicate, skilled work here as Kelly LaRock builds up the graphics, layer by layer. We learned a lot just shooting this video!

Tim Sanders, Wheatstone's resident craftsman, performs some very precise, very detailed hand work to give the LXE end panels the shine and deep color of a fine piano. You'll see every step of the process from the rough cut to the final finish in this video.

Here, at our computer-controlled metal press brake, flat metal that has previously been cut by the laser is precision-bent into its final shape. This machine is a marvel, capable of exerting tons of force, yet gentle enough to bend the thinnest of metal to tight tolerances. Here a back panel for one of the LXE control surfaces is being bent into its signature curve, one angle at a time.

Here’s a shot of Debbie, one of our hand assembly technicians, putting together the custom TS-4 panels used in the Panthers’ new system. This is where all the pieces come together: the acrylic front panel, the metal structure, the TS-4 circuit boards, and the connectors for mic and headphones. It’s incredible to see the care that goes into this assembly, leaving not a scratch, a tool mark, or even a fingerprint.

And here are those finished panels, all wrapped up in their protective plastic and ready to be boxed. That task is tackled by Erin in shipping and receiving. In that department, every piece of the system receives special attention to ensure that it ships safely and arrives just as beautiful as it was when it left the factory floor.

The finished LXE consoles receive special attention by the packing department. Here, the console is furnished with all its paperwork, accessories, and software, and wrapped in a snug plastic covering that will protect it from moisture and contamination during shipping.

Then it’s off to Erin again, where the console is nestled into its custom-designed foam and cardboard padding, and that in turn is packed in a sturdy cardboard crate. All to make sure the console arrives in perfect condition, ready to be unboxed, unwrapped, plugged in, and powered up.

The only thing missing from this OB studio is the BBQ grill!

Markus Stocker (known around here as “Swissy”) with Media Engineering in Switzerland developed this self-contained studio on wheels for stations to take on remotes. Instead of hauling around several flight cases, broadcasters simply roll in one prewired studio containing speakers, talkback, computer keyboard, playout system, mics, WiFi connectivity, codecs, and WheatNet-IP audio networking with two guest talent stations and split frame E-1 console. Notice the monitors (with Glass-E virtual mixer, so far-away engineers can remote in) mounted into the cover of the road case. Every station should have one!

More Photos of Portable Radio Rig

Your IP Question Answered

Q: I’m interested in AoIP for my facility, but I heard that I’ll need to regularly manage the streams. Is that true?

A: It’s true that older IP audio networks didn’t have an easy way to prune channel assigns. You’d have to delete these yourself periodically or get a bigger switch to handle an ever-increasing number of streams. That’s not the case with newer systems like WheatNet-IP, which continually prunes unused source groupings from the network so you don’t have to manually delete channel assignments that are no longer in use. No audio is passed or available on the WheatNet-IP network until it is requested. And when that request is closed, so is that audio channel. This eliminates you having to manage the streams, and dramatically reduces congestion and the possibility of packet collision/failure.

NAB 2018 Here We Come!

We’re Vegas bound with all the latest in audio processing, editing, IP networking and control surfaces. Stop in at booth N6806 and ask us about our new consoles and the very latest in virtualization. Industry observer Scott Fybush will be there to capture it all on video for those of you not attending NAB this year.

We’re looking forward to seeing you all in a few weeks and showing off some new shiny audio gear.

Kaden is in the House this NAB

Veteran major-market radio personality and power VoxPro user Kaden (@KADENRADIO) will be in Wheatstone booth N6806 this NAB to demo the latest VoxPro version and offer tips on how to rapidly edit phone calls in a PPM ratings world, in real-time. He will be in the booth at 11 a.m. and 2 p.m. Monday and Tuesday, and 11 a.m. Wednesday.

“VoxPro allows us to pack more personality into every call, and extremely fast," says Kaden, who takes hundreds of listener call-ins weekly. Currently located in Phoenix, he has a long and varied resume that includes positions at Entercom Communications, CBS Radio, and iHeartMedia with stints in Phoenix, Houston, Dallas, Minneapolis, New York City, among others.

Kaden on VoxPro7

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